1. Field of the Invention
The present invention relates to an electrically driven closure apparatus for architectures, such as an electrically-driven shutter of a building.
Generally, a closure apparatus having an electric motor to drive a closure member for opening and closing, for example, an entrance of a building has a risk of being jammed with an obstacle when being operated to close. Therefore, the apparatus preferably has an obstacle detector and an automatic stop controller that automatically stops the closure member when the obstacle detector detects the obstacle. Two types of the obstacle detector are known: one is a direct detecting type that detects an obstacle by a detecting sensor such as a seat plate switch provided on the closure member; the other is an indirect detecting type that detects an obstacle indirectly by detecting load variation or torque variation of the electric motor when the closure member is blocked by the obstacle. The indirect type detector has an advantage in that the closure member is not required to have an obstacle sensor and that the obstacle detector can also serve as a limit detector. Conventionally, the indirect type obstacle detector may detect the load variation in accordance with a variation of a rotation speed or an electric current value (or a voltage value). However, a general electric closure apparatus utilizes an electric motor working within a range where the variation of the rotation speed due to the load variation is small, so as to obtain a stable opening and closing speed. Therefore, there is a problem that the variation of the motor speed is small when the closure member is resisted by an obstacle. A problem experienced with the current detecting type is that the electric current can be varied by a disturbance rather than by the load variation. Thus, the above-mentioned detectors have difficulty in detecting an obstacle with high accuracy and good compatibility between detection sensitivity and operation stability.
In order to solve the above-described problem, a mechanism has been proposed which can perform stable opening and closing operation while detecting an obstacle accurately. In this mechanism, an electric motor or a driving device serves as a displaceable member that changes its position in accordance with the load variation. The displaceable member is supported by a load detecting spring (a neutral position keeping spring) that keeps, under a predetermined load, the displaceable member at a neutral position with respect to a fixed member that is fixed to a frame. A displacement sensor detects change in the position of the displaceable member against the load detecting spring.
However, the conventional load detecting spring mentioned above has substantially a U-shape with one end connected to the displaceable member and the other end connected to the fixed member. When the displaceable member changes the position against the spring constant between the both ends, the position change is detected by the displacement sensor. By changing the effective length of the load detecting spring, the spring constant can be changed so as to adjust the accuracy of detection of an obstacle. In this case, the spring constant of the conventional load detecting spring is adjusted by slidably attaching an adjustment member to the parallel portions of the U-shaped spring, so that the curved portion of the spring between the fixed points becomes ineffective. Therefore, the load detecting spring must have effective length large enough to provide the required spring constant and additional length for permitting attaching of the adjustment member. Moreover, the adjustment member must be attached so as not to allow twisting or deflection of the parallel portions of the spring. Thus, the load detecting spring as well as the adjustment member tends to become large.